A range of implements for striking objects exists. Such implements include tools (e.g., hammers, mallets, rug-beaters, etc.) as well as weapons (e.g., cudgels, truncheons, shillelaghs, etc.). Various types of sports equipment are among the striking implements operating in a similar fashion, i.e., by imparting an impulsive force to a struck object. The object may be, for example, a softball or baseball struck by a bat. Most implements for striking, including sports bats, are typically for manual use by an individual, e.g., a batter in a softball or baseball game who swings the bat. Sports bats are generally elongated shafts or tubes, of essentially circular cross section, having a longitudinal axis running the length of the shaft from a lower gripping end to an upper striking end.
Given that the utility of striking implements, and sports bats in particular, lies in their ability when swung to impart an impulsive force to a struck object, it is generally desirable that a bat, for instance, operate to impart to a ball as great a force as practicable under the circumstances during the brief period in which the bat and ball remain in contact. Application of force correlates with transfer of energy because work--a form of energy--is expressed as a force applied over a distance. Force, in turn, varies as the time derivative of momentum. Accordingly, increasing the amount of force applied by a bat to a struck ball will increase the amount of momentum and energy transfer between the bat and ball. As such energy will include kinetic energy--that is, energy related to motion--increasing the kinetic energy imparted to the ball will tend to increase the velocity of the ball and likewise the distance the ball can travel. In the games of softball and baseball, as in many sports involving a ball or other struck object, such an increase in velocity and distance traveled is highly desirable from a competitive standpoint and can confer competitive advantage on a game participant able to achieve such an increase (although safety concerns may place practical limitations on the maximum velocity which it is desirable for a ball to be capable of attaining).
In addition to maximizing the ability of a bat to transfer force under game-playing conditions, it is, more generally, desirable to provide a bat which a player may swing with relative ease to achieve a desired forceful impact between bat and ball. However, as such impact becomes more and more forceful stresses on the bat grow greater and greater, and so it is important as well to provide a bat which is durable and not readily subject to permanent malformation or structural failure as a result of such repeated forceful impacts. Those of ordinary skill in the art are aware that minimizing the thickness of the bat wall particularly at the anticipated point of bat-ball contact, proves advantageous because it maximizes the compression of the bat upon impact vis a vis the compression of the ball. Thicker bat walls do not compress as readily as thin walls, and, as compared to a thin bat wall in a collision between a thick bat wall and a ball, proportionately more of the compression which occurs takes place on the ball rather than the bat. This result is undesirable because ball compression and decompression results in significantly greater energy loss (e.g., as heat) than does bat compression and decompression. Accordingly, providing a bat wall thin enough to maximize bat compression vis a vis ball compression, but able to withstand structurally the repeated bat-ball impacts expected in normal use, would be an advantage over most known bats.
Currently-used softball bats may be made of metal, in particular, aluminum, for example C405 aluminum, which can also be used in construction of the bat of the instant invention. Currently-used bats have shell weights (i.e., the weight of the hollow aluminum shaft making up the exterior of the bat) of about 22 oz., but the most effective bat weight is known to be 28-30 oz. Substantially all existing bats increase the weight to this level by adding a load of 6-8 oz. to the end of the bat ("end loading"), embedded in a solid material (usually polyurethane).
Those in the sports equipment art have from time to time made various attempts to optimize bat design and performance. U.S. Pat. No. 514,420 to Jacobus disclosed a wooden bat having a carved-out axial portion into which one could place, for instance, ball bearings. Jacobus asserted such an arrangement would have two advantages: (A) easing strain on a batter's wrists while he waited for a pitch, as the ball bearings would be disposed in a lower position within the hollow and presumably exert less torque on the batter's wrists (torque being proportional to the distance at which a weight lies from a pivot point); and (B) increasing the (angular) momentum of the bat during a swing by allowing the ball bearings to move toward the upper end of the bat, thus enabling a more forcible blow. However, such an increase in angular momentum would result only from the application of additional exertion by the batter, as the bat would grow progressively more difficult to swing the further out the ball bearings moved along the axis.
Shroyer U.S. Pat. No. 1,499,128, teaches an all metal bat asserted to be more durable than wooden bats. The bat is hollow and has internal reinforcements for protection of the bat wall from the force of ball impact. Shroyer makes provision for a threaded axial aperture in the upper end of the bat, wherein a weight insert for adjusting the total bat weight to a desired value may be fixedly screwed.
Owen et al., U.S. Pat. No. 3,116,926, discloses a bat designed for developing a batter's wrist and arm strength by weighting the outer end of the bat, so as to increase torque about the batter's wrists and increase the effort required to swing the bat with a particular amount of angular momentum. Weights are fitted snugly into an axial chamber at the upper end of the bat and locked in place between an axial spring and a locking end-cap.
Johnson, U.S. Pat. No. 2,379,006, discloses (but does not claim) axial weight inserts snugly-fitted into a core portion of a bat formed of wood veneer, the inserts intended to balance the bat.
Fujii, U.S. Pat. No. 3,861,682, teaches a metal bat having a hard plastic insert disposed within for arresting the loud unpleasant metallic sound associated with impact of a metal bat. It also discloses an embodiment in which a metallic cylindrical repelling insertion member is provided in the inner periphery of the metallic bat shaft for structural reinforcement and sound arresting at the area of ball impact on the bat.
Peng, U.S. Pat. No. 4,951,948, discloses a bat asserted to provide superior shock absorption for prevention of injury to a batter. Peng uses a two-piece bat construction wherein a central handle portion is inserted into a main body portion, the two portions being connected at the upper end of the bat by a spring and snugly held by a retaining collar and elastic ring, or a gas bladder. The elastic retainer or gas bladder is asserted to provide a rebounding impulse force to the struck ball in that it compresses and then decompresses, thereby releasing upon decompression energy absorbed from ball impact shock.
Finally, Lewinski et al., U.S. Pat. No. 5,452,889, discloses a toy bat comprising a transparent shell partially filled with liquid for a splashing visual effect. Improved ball-striking characteristics are asserted to accrue from the centrifugal motion of the liquid toward the upper bat end during swinging.
In addition, efforts to evaluate and classify the performance of bats have demonstrated that certain analytical parameters are important for characterizing the ball-bat interaction in both a laboratory and a game setting. These parameters include basic physical quantities and locations such as the angular momentum, kinetic energy, and moment of inertia of the bat and the location of its Center of Percussion (the "COP", also correlated with the so-called "sweet spot" of the bat, i.e., the most desirable region on the bat surface for effectively hitting the ball), as well as derived parameters such as "coefficients of restitution" (CORs) for the bat and ball, as well as a "Bat Performance Factor" ("BPF"). A fuller description of a method and apparatus for defining and determining these and other parameters relating to the performance of a softball or baseball bat or similar sports equipment is found in my U.S. Pat. No. 5,672,809 (the "'809 Patent"), which I incorporate herein by reference.
As will be described more fully below in connection with certain comparative tests, based on computerized models and other evaluation methodologies related to my above-referenced bat testing method patent, I have found that existing attempts to improve bat performance do not achieve optimal results in terms of maximizing energy transfer from bat to ball so as to increase hit ball speed, making it comparatively easy for a batter to swing the bat rapidly to achieve a high angular momentum, and maximizing durability of the bat.
In particular, the above-described prior art patents reveal some attempts to achieve a more advantageous weight distribution within a bat, typically by providing weights at or near the upper end-cap of a bat (end loading), or located slightly below the end cap on the longitudinal axis in the interior of the bat. These weights may be rigidly fixed or in some cases movable along the longitudinal axis. Weights so situated do not optimize momentum or energy transfer upon striking a ball. Further, axially movable weights, to the extent they move out along the axis toward the upper end of the bat, tend to increase the moment of inertia of the bat, thus increasing the exertion a batter must apply to accelerate the bat for a powerful swing. Finally, while certain rigid or semi-rigid inserts exist for noise suppression and perhaps increasing durability of the bat, these known inserts do not provide significant momentum-transfer enhancement or facilitation of high-momentum swinging by the batter, and may, in fact, actually reduce momentum transfer.